Ken wrote:
> 
> Margus Ramst wrote:
> >
> > I believe Ken means light only enters the medium and is refracted if it is not
> > reflected. Light can be partially reflected or refracted, but only one of the
> > two can happen on a photon by photon basis.
> >
> > Margus
> 
> Ior is a property of a material. Reflection is a property of a surface. At least
> this was the rational for moving ior into it's own property wrapper i.e. interior.
> I know that surfaces can be considered to have an ior value but this is generaly
> a very minor property where roughness and color have a much greater impact than
> does a surfaces ior value will.
> 
>   To really clarify my point air does not generaly reflect light. It will transmit
> and refract light in varying amounts however. Shiny steel will reflect light redily
> but has extremely poor light transmittance.
> 
> --
> Ken Tyler
> 
> See my 700+ Povray and 3D Rendering and Raytracing Links at:
> http://home.pacbell.net/tylereng/index.html

	Well, actually I think that reflection depends on the ior (or rather on
the difference of iors between two materials) which in turn depends on
its electrical conductivity (is that the right word?). At least, that's
what happens when an electromagnetic wave hits a metal (please don't
think in photons as they are governed by quantic laws, which I'm not
familiar with): the electric field in the wave agitates the metal's
surface electrons creating an eletric current (since the metal is a
conductor) which in turn generates a new electromagnetic wave perfectly
in sync with the incoming one but of opposite sign. This wave is of
course emitted in all directions which means it *cancels* the incoming
wave inside the metal and creates what we call "reflection" outside.
When the material isn't as good an electrical conductor, the new wave
isn't as strong as the incoming one and that's what causes partial
reflection and refraction. Moreover the exact effect depends on the
angle between the *eletrical field* (not the direction of travel) and
the surface, therefore: angle dependant effects and polarization
dependant effects. This same effect causes absorption and scattering: as
the wave travels through a slightly conductive material, it will agitate
more and more electrons along the way and each time a small fraction of
the wave gets cancelled out and reemitted in other directions.

	Okay, there's just one problem with this model: I don't remember how it
accounts for materials like wood that neither reflect nor transmit any
light...

	Just my 2c,
		Jerome

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